<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    .triangle {
      position: relative;
    }

    .triangle::after {
      content: '';
      border: 4px solid transparent;
      border-top-color: #2c8ac2;
      position: absolute;
      top: 0;
    }
  </style>
</head>

<body>
  <div class="triangle"></div>
</body>

</html>